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.243 win based on AK innards

4K views 39 replies 6 participants last post by  TRX 
#1 ·
I drew up some plans for a rifle back in march and have been slowly collecting material and various parts as time/funds permit.




I'm starting with a TAPCO flat and the front end off an M70AB2. Originally, I was going to custom make the entire trunnion, but I thin I can modify the milled stub off the M70 easily to avoid a complete scratch build on the front trunnion.

I decided to go with G3 mags for the 243 shells. The reasoning behind this was the simple fact that I think they are cool as hell looking for a mag. :) The gas block/forward sight and muzzle attachement are also going to look a lot like a G3/HK, so they'll compliment each other.

I'm still undecided on the BCG. I'll probably just modify the M70 BCG. I might have to redo the upper half of the carrier to fit my low-profile needs, but doing that and redoing the piston shouldn't be too hard. Due to a longer gas tube, i was already going to have to redo the piston.

Forward grips will be made from 6061-T6 aluminum and freefloat around the barrel assembly. The barrel is a Rem mod-700 in 243 win. I cut it down to 17.5" and the muzzle is target crowned and outside threaded for 9/16"x24 (i already had those tap/die combo).

I finished my AK bending jig and got it tweaked so it bends the flats to an inside width of 1.245". To use the G3 mags, I'm going with a magwell. I bent up one using 0.032", 1050 steel. This is nice in that it fits just inside the AK frame when properly sized to fit the mags and when the dimples have been flattened. In the pic, it's still a bit large. It'll get the top 1/2" or so trimmed off and fit up into the frame higher than what you see here. I won't trim it until I get the trunnion made and mounted and the rails welded in. It took three tries to get the "perfect" magwell....I don't want to trim too much and screw it up!

I'll get to work on it next weekend...assuming my wife doesn't go into labor this week! ....even then, I still might get to work a bit. :)

Here's pics of the magwell fitting:



 
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#2 ·
have at it. I assume you have seen the converting to a 308 thread? there a lot of good info. Id recomend reloading and keeping the pressures down 243 max loads might be pushing it. now one has blown one up yet but you donet want to be the first its a pretty tight fit to get a G3 mag to work it will not fit into a m70 trunion as Is. Are you planing to trim the mag were the lower trunion rivots are? Im interested in what you do for a Mag latch.

Im going to be doing a 260 rem on a 308 sagia 3 lug bolt and trunion. it will be free floating barrel much like my other varmit builds. it will shoot full power loads. I toyed with 243 or even a 22-250 on a standard trunion I would be keeping the pressures down however.
 
#3 ·
I had originally planned on making my own trunnion and bolt. Looking at the milled stubs off the M70, I should be able to use those with no real problems. The whole trunnion assembly will be moved forward to accomodate the larger mag. The magwell section of the trunnion will get removed/opened up to fit the front of the custom magwell I made. The sides and bottom of the milled stub will be milled to fit the receiver flat. The original lower trunnion rivet hole will be one weld spot for the magwell. The other two rivet holes will be weld spots for the receiver flat to the newly milled trunnion. It may also get a rivet through it if I can find a spot that goes through the "meat" of the trunnion and doesn't interfere with the barrel.

I'm hoping the only mod I have to do to the mags is to dremmel down the rear face to allow for the bolt to slide over and strip a round easier. The AK bolt looks to hang down a bit lower than the G3. The mag release will be put where the open area is at the rear of the magwell. This will be similar to an AR-15...just a lever and spring that "clicks" into the catch opening on the side of the G3 mag. Mags will insert straight up into the magwell, not rocked in.

I plan on doing all reloads, although I can't see anywhere that 243 pressures would cause issues, maxing out at 60k. I'll probably be in the low to mid 50k with the loads/bullets I'm looking at. The lugs look plenty thick enough compared to several other 243 bolts I've looked at on bolt actions. Although that depends on jetal types and heat treat and such. I'm using a 1" dia chamber section on the remington barrel, plus the trunnion thickness. I think the gas adjustment may be the pain on this one. I'll start with a small hole and work up until I get proper function.

Hopefully Saturday I'll get more work done on it.
 
#4 ·
If you a using a standard 7.62x39 bolt and carrier, then if you move the front trunnion foward (about 3/8 of an inch I assume) the rear of the bolt will be too far foward. Which would allow the hammer to hit the center support instead of the firing pin.

I think, if I can remember right, so you might want to check it out.
 
#5 ·
Yeah, that was one reason I had planned on making my own bolt. I wasn't sure if I could just make a new hammer with a little more reach, or if I would need something more drastic like a whole new bolt. Witha new bolt, I'd just add the extra length to the end and make a new firing pin as well. I'd have to account for the extra boltlength when the BCG is in the fully rcoiled position. The recoil spring mount and rear trunnion would have to be customized for that, but that would be pretty easy. Support pins can always be relocated, so that doesn't concern me at all.

I get my springs and such in hopefully tomorrow. Then I can assemble the FCG and see what all I can do with a different hammer shape. The distance is more like a 1/2", so it's a pretty big alteration. The hammer would be longer with a slightly different angle on the upper end. The extention doesn't look like it will affect cocking/locking and there's plenty of overhead clearance, so it'll just be a bit of trial and error. The reduced spring tension with the extra rotation might be an issue, though. I'll be sure and take plenty of pics of all the mods as I do them.
 
#6 ·
This will be just like the .308 builds except of course for the barrel. You'll need to relocate the ejector.

You'll also have to move the center support back for the mag clearance. You may also have to enlarge the lower rivet area of the trunion for the bigger magazine. A FAL mag would provide better clearance and let you keep more of the meat on the trunion. Also would have a BHO feature similar to PSL :)

You can keep the FCG where it is but you'll have to reshape the front of the hammer to function properly with the center support being closer to it now.


Wasn't someone else working on a .243 build?
 
#7 ·
I was thinking that Aloharover was a 243, but it was a 308.
http://www.gunco.net/forums/f244/aloha-308-yugo-hybrid-24686/

Well in theory, if the front trunnion is moved forward, then the ejector might be fine in the stock postion. However the bolt/firing pin would need to be extended and have the ejector slot lenghtened in the bolt so that it would close and rotate into the locked postion. If you add material to the face of the hammer to reach the standard bolt, then you might have problems with clearence between the hammer and carrier when cycling.

On the other hand, if the trunnion stays in the standard place, then the ejector would need to be moved rearward and again the slot in the bolt lenghtened for the new ejector placement. Also moving the center support back to clear the mags can cause problems in that the hammer spring hits the support and keeps the hammer from being installed (learned that one the hard way).

Both ways have their pros and cons.
 
#8 ·
Instead of cutting rearward for mag clearance, I cut forward and chose to move the trunnion mounting location. Moving backwards looked like it caused more problems than fixed. The rear of the mag is in the exact same place as the AK mag, so the support pin won't need to be moved due to mag. Likewise, the ejector "should" work in it's present location. Due to a larger diameter shell base, I might could trim it a hair, but that'll be one of the last things I worry about. I didn't think about the bplt rotation with the ejector in a different position...thanks for pointing that out!:thumbup1:

Hammer mods can be one of two things......Thicken the hammer face to make up gap or lengthen hammer and allow for more rotation to allow proper strike. For a 1/2" gap, thickening the hammer face is out of the question. Instead, I'll lengthen the hammer and adjust the angle of the face to make up for the extra rotation needed for it to make contact with the firing pin. Unless, of course, I opt for building a new bolt.

I'll have to widen the cut out in the trunnion where the mag fits in. That's pretty easy to do. The meat on the walls of the trunnion stub in that spot don't concern me. I don't plan on riveting there. I was considering drilling a few holes or a slot, then backfilling with weld for the trunnion/receiver connection. There's a few locations I can stick a rivet as well. Once I get the trunnion stub fitted/located, I'll figure out exactly what I'll need for mounting.

Of course, once I've finished a couple months of planning and building I'll be heat treating the entire receiver, so if anything is going to screw up the build, it'll probably be that! Hah! I have a jig I'm making that should work pretty well for holding shape, though. It's basically a tapered I-beam That will insert into the receiver and screw onto the receiver. The custom rear trunnion will be on it as well during HT so that will help as well. All part of the fun, right!:rockin:
 
#9 ·
I plan on doing all reloads, although I can't see anywhere that 243 pressures would cause issues, maxing out at 60k. I'll probably be in the low to mid 50k with the loads/bullets I'm looking at. The lugs look plenty thick enough compared to several other 243 bolts I've looked at on bolt actions. Although that depends on jetal types and heat treat and such. I'm using a 1" dia chamber section on the remington barrel, plus the trunnion thickness. I think the gas adjustment may be the pain on this one. I'll start with a small hole and work up until I get proper function.
Be very aware that 2 lug fail the pressure tests required to allow there sale to the puplic in europe and likely here in the USA. that is why the the 308 Saiga has the third lug so it passes those proof tests. 60,000 PSI is a hell of a lot more pressure than the standard 7.62 round of around 43,000 PSI. also you need to factor in the differance in bolt thrust as the .243 round has a bigger case Bolt thrust is what you need t worry about that weaht the lugs see. I dont now what 243 you looked at that had simular sised lugs but every bolt action I have it much bigger. rem 700, win 70, mausers, rugger, savage are all much bigger. and have much more engagment area.

welding to the trunion is a really bad idea especialy on the upper area at that is were the lugs are. Any welding regardless how small it is is a stress riser I dont care if its the size of a bin head a weld affect the metal that it touches and the area directly nect to it most cracks start at a very very small inclusion or stress riser. I would not risk it especialy t the increased pressures as well as the recoil is greater meaning more pressure n rivets , screws or welds depending how you attaach the reciver. The m70 trunion from a stamped trunion has much more material than the Stubs from a milled kit. the trunion is not designed to add any strength to the barrel its there to hold the barrel and provide lugs for the bolt to push against.

This will be just like the .308 builds except of course for the barrel. You'll need to relocate the ejector.

You'll also have to move the center support back for the mag clearance. You may also have to enlarge the lower rivet area of the trunion for the bigger magazine. A FAL mag would provide better clearance and let you keep more of the meat on the trunion. Also would have a BHO feature similar to PSL

You can keep the FCG where it is but you'll have to reshape the front of the hammer to function properly with the center support being closer to it now.


Wasn't someone else working on a .243 build?

like he said. no reall differances from a 308 build .

you dont need to do all the mods your proposing simply move the ejector back. move the center support back cut the hammer to clear the new center support location, enlarge the bolt face, open up the ejection port on the dust cover, use a M70 bulged milled trunion for a little extra protection.

keep the loads at a lower pressure. 60,000 PSI will likely get you in trouble or dead. there are many MAX 243 loads at only 50,000PSI with certain powders, you should be able to find a good strong load in the 46,000 PSI range. i cant reach max loads with out pressure signs any way so its likely you can get a ggod load to suit your needs. what is the intended purpose for this build? what weight bullets do you intend to use.

the 243 is often facoty loaded hotter than a 308 because there are no old military weaker guns chamberd in it so the factorys dont have to worry as much.

the mag well you are using will work but it dont need to have it extnend into the trunion just stop it at the reciver bottom. if you trim the front of the mag it will fit you will need to rework the follower stop. the demples in the mag guide the round so the last 3/4" dont do any thing so that area can be lowered. I had one built up that would use a G3 but I ended up going with a FAL mag and never completed it with the G3 set up. the gs are cheap but they also are harder to get to feed right. I dont see any real differance in the clearance between a AK mag and a G3 as far as the bolt hitting it. in fact its nearly identical to a 223 in the clearance and just slightly shallower than a 7.62 round. a bulgy 223 bolt is the same as a normal x39 bolt so I see no need to cut the rear of the mag. it should catch the round no proplem. moving the magwell back takes up some finger clearance in the guard but if you use your style of mag well and ditch the stock AK style catch you gain most of it back as you will loose the are were the catch and the spring go.
 
#10 ·
I just read through the Aloha thread. I hadn't seen that one yet...what a cool build!

"Do you mean turn some threads on the back of the bolt, and then make up an extension, also threaded and just screw the extension onto the bolt?

That is a pretty cool idea."

I pulled the above from it. Hah....what an unbeleivably easy fix! Sometimes the simple things just get missed! Custom rear trunnion and mod to the ejector slot.

Man...now I feel like playing hookie from work to do some gunsmithing. Of course, my wife will be going into labor sometime in the next couple weeks. if I get the grandparents to watch the kids and change diapers...I can work on guns, right!?
 
#11 ·
I was just looking at the engagement on both the M70 and a MAK 90. I thought more of the lugs' surface area were in contact than that. That is a pretty small amount of area in contact.

I may go back to my original plan of making my own bolt/trunnion. Still a two lug design, but much larger lugs and surface area in contact.

The main loads I was looking at were 90 gr bullets and lower charges, but I'd like the option of much heavier loads. That of course would require the custom beefy design.

I'll post some schematics of the original design ideas this weekend.
 
#12 ·
I think you can get a pretty decent load with the right powders. I find on the Aks that I get pierced primers before I reach max loads especialy the 223. I recomend making a load up that is the hottest that can find run a mag through by string firing and recheck head space and recheck every so often with the normal lighter loads. watch out for bullets that are over size slightly as well. that will add pressure. I see some pretty decent loads that would IMOO be safe and are pretty fast compared to max loads that are often 10,000 PSI more. the short barrel you plan on using is going to make going to hot pointless any way as there likely will still be unburned powder. most of my guns shoot the best a grain or so under max anyways.

when kits were only $50 it was a very attractve to build a 308 or simular gun out of a AK kit but nw that there over $300 IMOO a Sagia cinversion is the better bet and it comes with a reciver and the correct bolt. I am collecting parts for a 22-250 fast twist barrel build that will be loaded lighter than the 65,000 PSI that those rounds can reach but it will still out run the 223 by a at least 250-300 fps with the heavier 70-80GR bullets I want to run. I want the case capacity needed to get the heavier bullets up to speed with lower pressure. theres a 6.5-300 savage wild cat in the works as well on a 2 lug trunion.

If you seriously have the machinery and skills and ability to properly machine and more importantly heat treat a bolt then simply make up a three lug bolt. it will fit in a staandard trunion. the 308 sagia is only slightly wider in the lug area or it would fit a Yugo trunion. while your at it make it longer in the front and then the barrel can be moved forward slightly. I think if a company or a individuale made some quality 3 lug bolts with big stems they would sell. I certanly would be interested in a few. If your not 1005 sure of the heat treat Id not attempt it. MY 50 BMG project is on hold untill I can get it dialed in. no gun is worth your face. the $500 or so for a used Sagia (I got mine for $350) is likley the better way to go I plan on loading my 260 remington conversion up to the max. I worry about the Saiga with three lugs holding. I havent heard of any coming apart the rest of the gun is crap as far as quality fit and finish and function. if it was some thing I didnt have a way to modify Id sell it. there very rough IMOO

good luck on the babby. hopefully in a bbout 10 years you can be fguring out how to do a 22 LR blow back for him or her. :)
 
#13 ·
Very nice!

If you're going to free-float the barrel, how do you plan to anchor the foregrip? Tight fit and retaining screw into the front of the trunnion?

Bolts have been extended before with no problem; also check Rahatakloom's 8mm conversion. You might be able to use a PSL firing pin.

I can't quite tell from your picture; the magwell looks like it might be galvanized steel. If so, you might want to practice a bit before welding it to your receiver. Galvanized is nasty stuff to weld.
 
#14 · (Edited)
Foregrip will be held by 4 screws on either side. Hopefully it will be rigid enough and not wobble out the holes in the aluminum grips with use. It's 6061-t6, so it should be pretty firm.

The magwell is 0.032" 1050 steel. It had surface rust and was sanded smooth with 400 grit wet sanding, so it has a mottled finish. The receiver will eventually be blasted and duracoated. I do knifemaking as well, so I have a hundred pounds or so of 1050, 1095 and L6 steels in sizes ranging from 0.025-0.057" that I use for making damascus/pattern-welded blades. I haven't done much in the last year due to work and moving so it's been sitting around in the Houston humidity! I'll be using some 0.057" for the trigger guard. After de-rusting, it'll probably be more like 0.045"! For welding, I'll use an aluminum block behind it as a heat sink and MIG weld it in several spots through small holes in the receiver, then grind flush on the exterior. 1050 isn't too bad to weld with mild-steel wire. The higher carbon stuff like 1095 and alloys like L6 are a pain unless you have a TIG welder.

As for heat treating, small items like bolts are no problem, provided they are out of a metal I'm used to doing (1050, 4130/40, 5160, 1095, L6, 440C, ATS-34, S30V). I'm limited to 7" long for my electric furnaces and 14" in the gas ones. I plan on making another furnace in the next few weeks that can do 18"L x 5"dia. Right now, the pain is that I have to make a trip up to Texas A&M to get access to rockwell hardness testers. I know how to get Rc 56-62 in all my steels....the 45-50 will take a bit of experimenting. I used to do axes out of 4130 and 4140. Pre-heat to 700* and hold for 10 min, bring up to 1600*F and soak at temp for 10min. Quench into Parks 50 until room temp, temper twice at 325* for two hours each. Rc-53-54. Little hard for a bolt, though. Most seem to be Rc 44-48.

My 10 yr old is getting a break-action single shot for early-Christmas in 357 MAX. I making an identical one, but slightly larger in .270 for my father. His will have color case hardened receiver flats. I've been doing a lot of experimenting with the coloring. Here's a couple links to videos using pretty crude, quick and dirty techniques for your entertainment...

[video=youtube;35sqJxcNrBQ]http://www.youtube.com/watch?v=35sqJxcNrBQ#lq-lq2-hq-vhq]YouTube - Color Case Hardening[/video]
[video=youtube;gwIq4nxQhyg]http://www.youtube.com/watch?v=gwIq4nxQhyg&NR=1]YouTube - color case hardening 2[/video]

The 5 yr old is next in line, but he's ready to start making his own. He likes the AKs!
 
#15 ·
good to know you not new at the heat treating and stuff.

instead of a a break open 357 maak why not a 7.62x25?? lot cheaper to shoot. Im looking at trying to sleave a handi rifle barrel with a take off barrel rechamberd into x25 for my son to shoot. looking for a small ring mauser action for the same round. I have him shooting plinker loads of red dot (around 6 grains ) in my military 30-06 and hes getting pretty good. I may try a insert or addapter but Im concerned with the corrosive ammo that I ight get some damage in the chamber of aa expensive barrel. was also a barrel insert in a shot gun barrel might be doable and dirt cheap and then he would have two guns in one. noting wrong with the 357 max but kids shoot a lot of ammo and the more they shoot the better they get. expense of the X25 is whit im thinking.

if H&R made a 7.62x25 handi rifle they would sell a million of them. I wish they would sell un chamberd barrels for there guns. Im looking for a 20 guage barrel to cut off and insert a rifle barrel through.

I added a brace under my 223 varmit builds fore grip from the reciver bottom its not pretty but it works and it floats.
 
#16 ·
Well, I got a 9mm barrel as pert of a group buy on another forum. It's been two months now and still no barrel, despite being told it been shipped twice now, so it may get a design change!

I'd thought about going with .44 mag since I'm set up to reload that already, it's got plenty of short-range knock down for hogs and the like, and I can find surplus barrels already chambered. There were several 7.62 cals I had considered, but inexpensive 30 cal barrels were hard to find. If I could find a heavy contour 30 cal chambered take-off barrel, I could just cut off the chamber and re-chamber. Everything seems to be "sportsman" contours that just doesn't leave much meat for rechambering. I kept finding some heavy Howa barrels on gunbroker, but they were always 1:12 twist and I wanted 1:10.

The tokarev is a pretty cool round. I had considered that one as well as 30 carbine.
 
#17 ·
that 1-12 twist might be better. the 30 benchrest guys use a slower twist than that even. 1-10 will stabelize a 210 GR bullet. I will never shot any thing that heavy. and as far as the 7.62x25 its under 100 gr. a sporting conture will have enough meat to cut off for a AK build. for a bolt action thats another matter. small ring action possably. I have a howa barrel sitting here that Im going to chamber into a .308x25 I didnt relize they were a 1-12 Ill have to check mine. thanks for the heads up. Id perfer it to be 1-12 for only a 125 GR bullet.

the main reasion I sugested the x25 is its around 10 cents per round. you cant reload any thing for that. its not a geat hunting round but I have seen hand loads listed in the 1800 fps range.

I just got a reamer for it and will be doing some chamberd blanks in the near future for sale or trade.

the M1 is just to expensive to consider and to weak for most hunting. a simple
7.62x39 rifle would be better and have more hunting uses plus ammo is while not cheap any more still pleanty avaliable.

what rifle were you going to use for this project or were you starting from scratch?? I like the NEF and H&R handirifles plus you can get lots of differant barrels for them. Rossi makes a cheap one but not as much of a selection. remington has one now to but Im not fermilular with it.

Kids are better off with out dealing with heavy recoil in a target shooting situation untill there big enough to handel it. I was shooting a 30-06 bolt action with no pad when I was 11 and it was tough to loose the flinch that it gave me. Dad used to make me sight it in my self. I would have been better just shooting it in a hunting situation were the recoil is not felt so much due to adrenelin. I remember shooting 5 shots at a running buck getting it and not even noticing my cut eye from the scope or the bruises on my shoulder. a chamber insert would have been a good start for me with that rifle or reduced plinker loads Like I have my 9 year old shooting at paper.
 
#18 ·
My .308 conversion experience is documented here on the caliber conversion forum and on my website:

http://pookieweb.dyndns.org:61129/AKM/AK_308/ak_308.htm

NOte that the conversion challenges I mentioned are the same things the Russians did with the .308 Saiga. So if you find any posts anywhere about the differences on a .308 Saiga vs. standard AK, you'll have everything you need.

It is very obvious what you'll need to do if you start with the front of the mag and trunion and work back from there; you'll encounter every one of the changes that you need to make. :)

Personally I am not worried about putting my face near a .308-family conversion after seeing the Yugo .308 solution is basically to open up the rim of the bolt face. Those huge locking lugs are IMO over-engineered for what they do. Now of course I'm not going to tell anyone else to put THEIR face near a .308-family conversion because you can never tell when Mr. Murphy will show up... so do be careful!

Like biggun said if you don't get too hot with the loads you should be OK. I would think accuracy is a higher priority than sheer velocity, so you probably won't even use a really hot load anyway. I would not recommend loads that land on the right-hand side of the charts! Stay away from the red line and you *should* be OK.
 
#19 ·
10 cents a round is always nice! I let my son shoot my Russian M44 this past weekend. I sporterized it with a larger buttstock and recoil pad. His expression was priceless. He said it didn't hurt, but I think his whole body moved back about a foot!

I have two single shot scratch builds in progress. I'll be picking up a couple parts Sunday that I had someone else do on their lathe. These are complete scratch builds. Everything is being made from raw material. Most of it is 1050 steel with A2 being used for some of the FCG parts. The 270 version uses a rem700 barrel. The other is planned for 357 MAX. For plinking 38 spl could be used in it also. Of course, I may opt to go with another barrel/cal if I don't get word on the other one! I should get a little work done on them this Sunday and get some pics. I have everything to finish out the 270 now.

I decided to make my own bolt and carrier for the 243. I'll use the M70 and/or MAK-90 as a template for most of the cuts. The front of the bolt is going to extend out some. This will put the hammer/iring pin back into the correct positions as well as allow me to do a third lug easily. The front trunnion is being made custom as well. Pretty much identical as the stock one, but with a slight mod to the lower left section (left when facing chamber). I might dicker witht the rotation since the rotation extension won't be part of the lug anymore. I can probably get another 10* of rotation for more lock-up surface area.

Looking over most of the load data for the 243, I envision being in the 46-48K CUP zone. Maybe up into 50-51K. I have no experience reloading 243, but 300 WM and 44 Mag seem to work best at about 85% and 75% max loads. There were some loads developed by encore shooters with 15-18" barrels that I've been mostly looking at since I plan on using 18" barrel.
 
#20 ·
You're going to make the front trunnion, bolt, and bolt carrier?

I spent some time earlier this year sussing out the machining steps for those parts, and decided my round tuit list is long enough that my current project would never get completed if I got sidetracked that far.

The bolt is fairly straightforward. Some Valmets, Galils, and Norincos came with a different firing pin and an internal spring to keep the firing pin from dinging the primer when the bolt comes into battery; not a problem with Commie military ammo, but it'd be a nice extra bit of safety for softer civilian primers. The couple of bolts I have on hand look like the spaces between the lugs were just gnawed out with small end mills, not particularly sharp. It doesn't matter since the only part of the bolt head that counts is the lugs; the rest is just cut back for clearance. Startling after looking at Mauser or Remington bolts, though. There's a thread over in the Saiga subforum with some good pictures of the Saiga 3-lug bolt. They just added some meat to the ramp that normally slides over the top of the cartridge when the bolt moves back. Damned if I can see why it doesn't ding up the shoulder, but it appears to work.

You can do most of the internal cuts in the front trunnion with standard keyseat cutters, though you might have to grind the shanks a bit to clear the trunnion. The trunnion has a lot of cuts that don't serve any mechanical purpose for the firearm. I originally thought they were lightening cuts, but my new theory is that they're intended to reduce thick sections that might cause problems with the heat treat. Also, looking at the Yugo trunnion by my keyboard, it looks like the front was faced off on a lathe. Presumably the barrel hole was bored at this time, and all other dimensions and machining ops came from the front and the hole centerline.

If you're using a manual mill, some of the cuts in the trunnion will be "blind", with only the crank dials or DRO telling you where you are.

The bolt carrier is more complex than it looks. It will need lathe ops to do the spring hole and snout, then you'll have to make a jig to hold it to a virtual center along the centerline of the bolt and cut the internal cam groove. You could do it by hand with plenty of patience, but normally you'd need a 4th axis on a mill table.

Both (or all three) of the locking lugs are in different planes. I'm not sure why this was done, and it surely complicates duplicating the original. Someone may know and interject the reason; otherwise, I'd think about just putting them all in the same plane, and then you could cut all three locking faces in the trunnion on the same setup.

For your .243, I'd recommend using the thicker Yugo-style receiver and duplicating the Yugo trunnion, which is narrower, has a different rivet pattern, and appears to be stronger around the locking lug area.
 
#21 ·
Cool, thanks to everyone for the info and links! Being low on funds, and making the bolt...I might as well make the others also. It's been almost 20 yrs since I woked as a machinist, so I need the practice for some upcoming projects!!! After talking this evening with the guy who owns the mill, we're going to transport it over to my place and set it up this weekend so I'll have unlimited use for a couple months or so. :rockin:

I'll have to check out the saiga bolt. Sounds like what I plan on doing is pretty much what they did. I'm making the third lug from the bottom section. Adding the forward extension allows me to keep the same thickness/depth of the section while making a lug out of the forward most section of it. I couldn't figure out why the lugs were offset from each other either. Mine will all be the same plane.

I've been looking over the trunnion section. It seems pretty straight forward. There's a few cuts I won't bo doing since I'm altering it a little. There's lots of tooling marks left in the yugo one, so it wasn't too bad to figure out what tools and from what direction cuts were made. Some of the cuts look like they were made to allow room for the other bits to come in from a different direction and serve no other function. There's a few spots where I can beef it up without causing bolt interference. I figure a lot of it's going to be "cut to fit" until everything is where I want it and it locks up properly. The barrel can be moved in and out for the final headspacing. I'm using a block of O1 tool steel which isn't bad about warping during heat treat and is through-hardening and easy to get down into the spring hardness levels. I'll take photos of all the set-ups and tooling as I do it. If it all works, there'll be a nice photo-how-to...if it doesn't work, well, there'll be a nice photo-how-not-to!

After studying the carrier and seeing how they did their's, man what a pain. Looks like it was done starting with some round stock and the main bolt hole done. After that, anything that doesn't look like a bolt was milled off. Not really difficult cuts...just very time consuming when the mill I'm using is a smaller one and can't do thick passes. I did some .050" cuts when doing a FAL upper and it liked to have killed the machine! I think I might just get a carrier. I have one, but since I won't be scavenging the other parts, I want to keep it with the rest of the M70 parts and just make the M70 at some point. Carriers pop up regularly on gunbroker for ~$25-35.
 
#22 ·
When I first took an AK apart I saw all the machine marks from dull cutters and thought, "Man, why didn't they just do all these parts as investment castings?" Darned if I can find any sprue marks anywhere on the parts I have, nor can I come up with a reason why they'd duplicate such cobby machine work. If all you have to do is one part for a pattern, why not make it nice?

I have a milled receiver on hand, and it looks for all the world like they took a Big Chunk O' Steel and whittled 90% of it away. WTF? No wonder it looks like the cutters were dull...

Oh, and for something practical - if you build the back using a narrowed AKM rear trunnion, you can use AKM stocks if you narrow the spigot slightly. The selection of fixed stocks to fit the Yugo receiver is small, and prices are considerably more than AKM stuff. And Yugo trunnions are expensive, too.

I love the looks of the Yugo underfolder, but I just couldn't come to terms with the idea of firing a big bore cartridge with a T-shirt and the Yugo's horseshoe-shaped buttplate.
 
#23 ·
I would think accuracy is a higher priority than sheer velocity, so you probably won't even use a really hot load anyway. I would not recommend loads that land on the right-hand side of the charts! Stay away from the red line and you *should* be OK.
I agree and most of my most accurate loads under max. running fast powders to maximise a short barrel can get trickey and possably dangerious. The advantage of a 308 or in this case a 243 is more case capacity to burn a slower powder to get higher speeds at less pressure.

If I were going to make any thing Id concentrate on the bolt. the trunion and carrier are all still avaliable releativly inexpensivly. a saiga bolt is slightly wider across the two lugs than a standard and has the bottom area were it slides over the mag extended down. I would not change the length or any thing else except possably the stem size so it fits a larger carrier, id just copy it just slightly narrower across the lugs to fit a standard trunion. If you can make all of it more power to you.

if you do a trunion make it for a threaded barrel with a larger ID so a big bre acn be done. some thing like the threads on a M70 Win barrel would be nice.
 
#25 ·
Got quite a bit of shop time this past week. Mostly finishing up some knife projects, but did a bit on the rilfe as well.

I got the block fit into the magwell where the mag ejector with be. I'll do the trigger guard and pistolgrip mounting nut tomorrow.

I got quite a bit done on the trunnion. Most of time was spent working out exactly what I wanted to do with regards to what gets extended/modified. Once that was worked out, the rest of the time was just standing there at the mill. I borrowed a mini-mill for a couple months, so I'm limited on tooling and thickness of cuts. 90% of my tooling is HSS. It did NOT like normalized steel of any alloy. I have four projects going on at once and all use medium carbon steel and alloy steel. I broke down and just spent a day doing annealing cycles. Below are a couple pics of the process.




First, marry a woman that loves you and accepts your hobbies, then drag your furnace inside and set it up on the kitchen counter if that's the only 20 A breaker in the house. :)

I put in the biggest hunks and brought the peices up to 1575*F, and let soak long enough to ensure they were heated throughout. Then I shoved in all the other parts and let eaqualize at 1575*. I next brought it down to 1400* and held for four hours. Then, I turned off the furnace and let cool down overnight (~10 hours). The parts were still about 350* 10 hours later. Man, what a diffwerence it made on the 4130!
 
#26 ·
I started to use a hunk of O1 for the trunnion, but it wasn't wide enough to do what I wanted, plus it's a bitch to machine. I have a huge hunk of 4130 I use as a sharp-cornered object with my forgework and knifemaking. It's just a 2 x 4 x 10 hunk. My dad took his chopsaw back, my cutoff bandsaw died last year...so I just used the drill press and an angle grinder with cutoff disks.



The resulting hunk was one of the blocks in the above annealing pics. After that, I flattened all the surfaces and brought it down to the starting size I wanted. I used the M70AB2 as a template...kind of. I widened the whole thing by 0.050" and my locking shoulders will all be in the same plane. I blued it with ink and scribed several reference lines.



After making the rectangular block, I did the upper main cutout. This makes it easy to mark and measure the next couple cuts.



After that, I began roughing out the upper half of the opening. In order to keep small radius corners, I did this with a 1/4" endmill. In the annealed state, I was taking 0.035" cuts...which is pretty good for one of these mini-mills on steel! Here's where I stopped this evening. Next, I'll slot the walls. The surface there is where the rail surfaces will line up. It makes a nice guide for the keyway cutter.



Next, I'll do the barrel hole....maybe. I'm hoping I can use a 4 jaw, independent jaw chuck on a small lathe and chuck it up. This would make very short work of the barrel hole and the locking shoulders. "IF" it works, I'll start with some large deming bits and open it up to 63/64th ( no particular reason other than that's what I have). Then I'll chuck up a 1" mill bit and ream it all the way down to where the shoulders are. Then, I'll go back to the mill, do the underside cutouts and clean up some of the corners and finish out the remaining cuts.

P.S. Ideally, you'd do the hole first. For one, it's easier to drill/mill out a hole in a symmetric block. Secondly, if you screw it up, you can mill the block down until the hole is centered where you want it...and if you totally blow it...there's not much time invested in it yet.
 
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